Resist materials used for etching, plating and the like in the field of manufacturing printed wiring boards include widely employed photosensitive resin compositions and photosensitive elements obtained by laminating these onto supports and covering them with protective films.
When a photosensitive element is used to produce a printed wiring board, first the photosensitive element is laminated on a circuit-forming board such as a copper substrate while releasing the protective film, to laminate a photosensitive resin composition layer composed of a photosensitive resin composition on the circuit-forming board. Next, the photosensitive resin composition layer is subjected to pattern exposure through a mask film or the like, and then the unexposed sections of the photosensitive resin composition layer are removed with a developing solution to form a resist pattern. Next, the resist pattern is used as a mask for etching or plating of the circuit-forming board on which the resist pattern has been formed, to form a circuit pattern, and finally the cured sections of the photosensitive resin composition layer (resist pattern) are released and removed from the circuit-forming board.
Such printed wiring board manufacturing methods implement laser direct writing method, whereby active light rays are directly irradiated in an image using digital data, without a mask film. The light source for the laser direct writing is a YAG laser, semiconductor laser or the like, for safety and manageability. In recent years it has also been proposed to employ gallium nitride-based blue laser and similar light sources, that have long usable life and high output.
Also recently, DLP (Digital Light Processing) exposure has been studied as a laser direct writing method that allows formation of finer patterns than in the past, for suitability to high definition and high density of semiconductor package printed wiring boards. Generally speaking, DLP exposure uses active light rays with a wavelength of 390-430 nm, with a violet semiconductor laser as the light source. For general purpose printed wiring boards there are mainly used exposure methods that employ polygon multibeams with wavelengths of 355 nm from a YAG laser light source, which are suitable for small-batch, multi-variety products.
Several types of sensitizing agents are used in photosensitive resin compositions to match the different wavelengths of light sources in laser direct writing methods (see Patent documents 1 and 2).